The present invention relates to an apparatus for inspecting a component or a printed circuit board device.
Apparatus for inspecting a printed circuit board device enables a variety of features of a printed circuit board device to be inspected including, for example, the quality of solder joints and the placement and different features of the components. During inspection of solder joints, defects can be detected and categorized into defect types, such as solder bridging or shorting, no solder, insufficient solder, de-wetted solder, void in solder, excessive solder, and tombstoning. The types of defects which can occur in the placement and with regard to the features of components include amongst others wrong orientation or polarity of the component, misalignment of the component, missing component, incorrect component type, wrong component value, wrong component marking, and inverted component.
There are major differences between the visual appearance of solder joints and the visual appearance of components. Typically, solder joints are highly reflective (shiny) and posses certain distinguishable three-dimensional shapes, whereas the visual appearance of components is characterized by large variations in color, surface texture, shape, and height. Components also tend to include identification markings, which can vary widely, to represent features such as polarity, orientation, value, part number and so on. Some polarity identifications are represented by a color, a bar, a dimple, or characters. Laser marking is an increasingly popular method of generating identification markings on components.
In prior art apparatus for inspecting a printed circuit board device, various colors will correspond to images produced at different elevations relative to the printed circuit board under inspection to produce a mapping which constitutes a three dimensional representation of a two dimensional image providing a significantly enhanced image for visual inspection purposes. By analyzing the smoothness of the transitions from one topographical zone to the next, a measure of solder wetting can be made. By detecting aberrations or secondary shapes, voids, blow holes and pinholes may be detected. Thus, significant information may be developed by performing weighted calculations.
U.S. Pat. No. 5,039,868 discloses a substrate inspection apparatus comprising light projecting means including a plurality of ring-shaped sources for directing light of different hues to a part obliquely from one direction at different angles of incidence, first imaging means including a color camera for imaging reflected light from the surface of a portion to be inspected by hues on the center line of each of the right-shaped light sources in a position directly over the part. There is no provision to independently control each of the light sources.
U.S. Pat. No. 4,677,473 describes a soldering inspection system wherein light is irradiated on a soldered part at different incident angles by a light emitting means to collect information indicative of three-dimensional configuration of the soldered part and discriminate whether or not the configuration is acceptable. The three-dimensional configurational information can be obtained with light irradiated at least from two positions mutually of different angles with respect to the soldered part. The inspection is thereby made from a quantitative viewpoint.
U.S. Pat. No. 5,060,065 discloses a printed circuit board inspection device including a lighting system for use with a series of cameras associated with the inspection device, the lighting system being essentially domed in configuration and incorporating a plurality of selectively controllable light emitting diodes for developing desired lighting patterns. The light emitting diodes are arranged within the domed fixture to form an array of defined latitudes and longitudes and are capable of selective activation to develop the particular lighting patterns which are desired. This permits acquisition of images useful in developing a “topographical display” of the acquired image, which is useful in enhancing the subsequent inspections which are to be performed. The domed fixture is integrally formed and has a predetermined arrangement of light elements of different light characteristics and orientations of projection for creating a predetermined illumination pattern. Therefore, different models of domed fixtures need to be manufactured for different applications, and the whole domed fixture has to be replaced for another application.